Liquid filtration device

ABSTRACT

The present invention provides a liquid filtration device with internal flow paths that facilitate the purging of air bubbles from the device. The device includes internal channels that collect bubbles from fluid entering the filtration device and more efficiently direct fluid to sweep bubbles from the device during operation. The present invention also provides for an automatic means to minimize fluid loss during a vent process.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/380,314, filed Mar. 12, 2003, which is the U.S. National Stage ofInternational Application No. PCT/US01/028771, filed Sep. 13, 2001,published in English, which claims the benefit of U.S. Application No.60/232,209, filed on Sep. 13, 2000. The entire teachings of the aboveapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The IMPACT® LVHD filter, sold by Mykrolis Corporation of Bedford, Mass.,has a low hold up volume which is very advantageous due to the high costof the process fluids principally filtered by the device: photoresist,dielectrics, anti-reflectives and optical disc materials. The IMPACTLHVD filter provides superior filtration to prevent debris in theprocess fluid from being deposited onto the substrate and from causingdefects.

A sectional view of the current IMPACT filter may be found in FIG. 1.FIG. 1 provides a device that uses three independent connections, a vent12, a feed 14, and an outlet 16, that can interface with either a standalone manifold or directly to a dispense system such as the RGEN™ orIntelliGen® dispense systems that are manufactured by MykrolisCorporation. The process fluid enters through the inlet port 14 andflows through the inlet tube 24 to the housing bottom 25. The processfluid then flows through the vertical membrane filter 26 to the outletport 16, where the purified fluid is directed back to the manifold ordispense system. The vent port 12 allows bubbles that accumulate on theupstream side of the filter to exit the housing 22. To better eliminatebubbles from the filter, the top surface of the housing cap 18 is set atan angle directed up to the vent port 12. This allows air bubbles togradually rise to the highest point in the housing 20 and to exit thehousing 22.

A more detailed description of the attributes and benefits of the IMPACTLHVD filter may be found in Mykrolis Applications Note No. MA068entitled “New Photochemical Filtration Technology for ProcessImprovement” by M. Clarke and Kwok-Shun Cheng. This paper was originallypresented at the INTERFACE '97 Poster Session on Nov. 10, 1997. Also,benefits of the IMPACT LHVD are presented in Mykrolis Applications NoteNo. MAL109 entitled “Improving Photolithography Equipment OEE with theIMPACT ST Manifold” by M. Clarke.

Although the design and performance of the IMPACT LHVD filter is muchimproved over other filtration devices, it is also not fully optimizedfor bubble venting. In the IMPACT LHVD filter, bubble-laden fluid isforced to the bottom of the device to sweep the bottom with fluid toprevent fluid stagnation at the bottom and the formation of gelparticles. Therefore, any entrained bubbles must then rise to the vent.Again, the slowly rising bubbles from the bottom will require more timeand chemical to purge them from the device.

To compensate for the shortcomings of filters and how they are used instandard filtration and dispense systems, Mykrolis developed integratedfiltration and dispense systems called “Two Stage Technology” or “TST”.The designs of these TST systems allow for recirculation of bubble-ladenfluid to minimize the amount of fluid that is wasted during start-up ofa new filter. Although these systems more efficiently remove bubblesfrom the filter and conserve fluid, waste is still generated, as theventing process is not optimized.

A more detailed description of the operation of a Two Stage TechnologySystem is given in Mykrolis Applications Note No. MAL111 entitled“Understanding the Operating Cycles of Millipore Two-Stage TechnologyPhotochemical Dispense Systems” by M. Clarke.

For all of these systems (even including TST systems), bubble venting isstill not optimized as the venting process release not just bubbles buta bubble saturated fluid stream. Since bubbles do not rise quickly inmany process fluids, the motion of the fluid toward the vent is requiredto remove the bubbles (effectively, the bubbles are carried along by thefluid stream). In addition, the smaller the bubbles to be removed, themore fluid that is ejected in the stream.

It is apparent from the aforementioned applications notes anddiscussions that gas bubbles are a concern to semiconductormanufacturers. However, the current IMPACT filter or any other currentlyavailable product, inadequately addresses the need to sweep bubbles fromall surfaces of the filtration device as well as to initiate bubbleremoval prior to filtration.

Accordingly, it would be desirable to provide a liquid filtration devicewherein bubble removal from the liquid being filtered be initiated priorto filtration so that the gas bubbles removed are positioned near thevent, thereby facilitating gas bubble removal from the liquid beingfiltered. Also, it would be desirable to have the system to provide ameans for automatic venting of a liquid filtration device that minimizesthe amount of fluid loss.

SUMMARY OF THE INVENTION

The present invention provides a device that eliminates gas bubbles froma fluid by using the fluid's velocity within the device, coupled withspecific flow channels, to remove pockets of gas from liquid filtrationdevices. The properly designed flow paths direct fluid into locationswhere gas bubbles will most likely collect.

The present invention provides a device and method for eliminating gasbubbles from a liquid within a housing having a housing cover that willallow for faster and more efficient removal of entrained bubbles. Thenew device and method uses a portion of the fluid's velocity at thedevice inlet to sweep around the underside of a flange of a filtercartridge within the device. This will force gas bubbles within thefluid to rise above the filter membrane and adjacent the inside surfaceof the housing cover. The liquid streams positioned beneath the filtercartridge's flange then converge to the inside surface of the housingcover and proceed to force gas bubbles from the fluid to proceed towardthe vent port of the device.

In addition, the present invention provides a method for effectingautomatic venting of bubbles from the fluid being filtered.

It is an object of the present invention to provide a liquid filtrationdevice that eliminates gas bubbles from fluid within the device during avent cycle.

It is also an object of the present invention to provide a liquidfiltration device that removes gas bubbles from a fluid by utilizingsurfaces in the device while the device is operated in a filtrationcycle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of the prior art, a sectional view of anIMPACT LHVD filter.

FIGS. 2 a and 2 b are cross-sectional views of the filtration device ofthe present invention with arrows representing fluid flow paths.

FIG. 3 a is a view of the underside of the top cap of the filtrationdevice of this invention.

FIG. 3 b is a partial cross sectional view of the top cap of FIG. 3 apositioned relative to a cap on the filter cartridge of this invention.

FIG. 4 a is a partial sectional view of the present invention whichshows fluid channels with arrow representing fluid flow paths.

FIG. 4 b is an underside view of the device of FIG. 4 a.

FIG. 5 is a top view of the bowl of the filtration device of the presentinvention.

FIG. 6 a is a partial section view of the present invention which showsfluid channels with arrow representation of the fluid flow path.

FIG. 6 b is an underside view of the device of FIG. 6 a.

FIG. 7 is an underside view of the top cap and housing with arrowsrepresenting the fluid flow paths.

FIG. 8 is a partial sectional view of the present invention which showsa fluid channel and arrow representations of fluid flow paths.

FIG. 9 is a partial sectional view of the present invention which showsa fluid channel and the convergence of fluid flow paths access point toforce air bubbles above filter cartridge.

FIG. 10 is a bottom view of an alternative housing cover of thisinvention.

FIG. 11 is a bottom view of an alternative top cap of this inventionused in conjunction with the housing cover of FIG. 10.

FIG. 12 is a flow diagram illustrating an automated method for operatingthe device of this invention.

DETAILED DESCRIPTION OF THE INVENTION

The flow direction of both bubbles removed from fluid being filtered andthe filtered fluid within the filtration device of this inventiondepends upon the mode in which the device is being operated. Thefiltration device of this invention can be operated with the vent eitheropen or closed. In an initial operating mode of the filtration device,the filtration device is filled with fluid and additional fluid ispumped through the device with the vent open to remove the majority ofgas and bubbles from the device. During this mode of operation,bubble-laden fluid is also passed through the vent. Subsequent to thisinitial mode of operation, the vent is closed and the fluid beingfiltered is pumped through the filter device of this invention. Duringthis mode, bubbles are constantly separated from the fluid beingfiltered and are collected at or near the vent. In a preferred mode ofoperation, fluid is recirculated through the filtration device for aperiod of time to assure complete or substantially complete gas removalfrom the pores of the filter to minimize the amount of fluid that iswasted. At specific intervals, the vent is opened and bubbles areexpelled from the filtration device. The vent then is closed andbubble-free fluid can be dispensed to a point of use. After some periodof time, the device will collect additional bubbles and another ventoperation is needed. Again, bubbles and fluid will be expelled throughthe vent.

The bubbles entrained within the fluid are forced from the fluid alongone of two locations within the filtration device. A first channel ispositioned in a housing cover of the filtration device and is positionedto be in direct fluid communication with the vent. A second channel ispositioned in a top cap above the filter membrane of the filtrationdevice and is positioned to be in direct fluid communication with thefirst channel. The first channel accumulates bubbles from the fluid asthe fluid enters the filtration device. The first channel also ispositioned to accept bubbles recovered in the second channel. The secondchannel accumulates any bubbles that either collect or form on theupstream side of the filtration membrane of the filtration device. Thus,the filtration device recovers bubbles which are immediately releasedfrom the fluid upon entering the filtration device and which arereleased from the fluid prior to filtration.

The present invention provides a liquid filtration device with internalflow paths that facilitate the removal of air bubbles therefrom, thedevice comprising a housing, said housing including a bowl; a cap and acover, the cover having internal and external surfaces and characterizedby apertures therein that serve as fluid inlet, outlet and a vent,whereby said cap, cover and bowl are combined in such a manner thatfluid channels are created, such channels facilitating sweeping bubblesout of the device and toward the vent, said channels including a fluidchannel that directs fluid toward that portion of the housing where thevent is located; a fluid channel that directs fluid to sweep the bottomof the bowl; and a fluid channel that directs fluid to sweep theundersurface of the cap.

In a preferred embodiment, the device is designed so that the inlet andvent fluid flow path cross-sectional areas are controlled in a mannersuch that an optimal fluid velocity is achieved for bubble removal andseparation, thereby increasing the efficiency of bubble removal.

In a preferred embodiment, the underside of said top cap has a slopingsurface, said sloping surface having a nadir and zenith which isutilized during venting and filtration cycles as well as between cycles.Such a sloping surface will facilitate removal of bubble from thedevice. Preferably, the surface zenith is juxtaposed to the ventaperture so the bubbles are more efficiently removed from the fluid.

In a preferred embodiment, vent paths will converge at or near the nadirof the volume between the cap and the cover. It is understood that thisvolume will be where air bubbles to be purged will congregate.Preferably for this embodiment, the surface zenith is juxtaposed to thevent aperture so the bubbles are more efficiently removed.

In a preferred embodiment of the present invention, the internal surfaceof the cover will have a vent ridge, the zenith of said vent ridgepositioned substantially near the vent aperture.

In another preferred embodiment, the vent is located directly above avent aperture while restricting the vent fluid path to maintain fluidvelocity to force gas from the fluid.

In another preferred embodiment, the vent process is automaticallycontrolled such that minimal fluid is lost during the vent process.

The present invention provides a method of removing air bubbles from adevice intended to filter fluid, said device including an inlet, outletand vent and said device characterized by being subjected to filtrationand vent processes, the method comprising providing fluid channels thatare swept during filtration and vent processes. Fluid channels areprovided that facilitate the sweeping of air bubbles from the surfacesof the device towards a vent, whereby use of the device in eitherfiltration or venting will remove air bubbles from the device.

Referring to FIGS. 2 a and 2 b, a device of the present inventionincludes an outlet 30, an inlet 32 and a vent 34 that are formed fromthe housing cover 36. The housing cover 36 is fitted to the top cap 38and housing bowl 42. Filter media 40 is contained within the housingbowl 42. The arrows indicate how fluid will flow in the device. Diverter44 alters the fluid flow path from the inlet towards the vent 34. Whenthe filtration device is filtering fluid, the majority of the fluid willpass directly from the inlet 32 to the housing bowl 42 while depositingair bubbles in the vicinity of the vent 34. The housing cover 36 isprovided with a first channel 31 which extends about the entire orsubstantially entire circumference of housing cover 36 and provides apathway for gas and bubbles to be directed to vent 34. The top cap 38 isprovided with a second channel 33 which extends substantially the entirecircumference of top cap 38 and provides a pathway for gas from inletfluid to be directed into the first channel 31 and then through vent 34.

Referring to FIGS. 3 a and 3 b, the housing cover 36 has its internalsurface 37 angled towards the vent side 35 of the housing cover 36. Thefirst channel 31 spirals up from the outlet side 39 of the housing cover36 to the vent 34 (FIG. 2 b) to remove all additional gas bubbles.

Also, as shown in FIGS. 3 a and 3 b, inlet fluid is redirected from thecenter of the housing to the side of the housing by the diverter 44where the vent 34 (FIG. 2 b) is located for this particular design. Thisconfiguration forces bubble-laden fluid from the inlet 32 (FIG. 2 b) totravel towards the vent 34 (FIG. 2 b). By controlling thecross-sectional area, the fluid velocity can be regulated such thatbuoyant forces and residence time are optimized for efficient bubbleremoval. The fluid then travels down the side fluid channel 46.

FIGS. 4 a and 4 b illustrate the inlet fluid being directed below thetop cap 38 (FIG. 2 b) through the cut out 52 where it then is split off.Most of the fluid travels down the side fluid channel 46 created withtwo ribs 49 found on the inside of the bowl 42 (FIG. 2 b) to sweep thehousing bowl bottom 25 (FIG. 6 b) to prevent stagnant fluid locationsand the formation of gel particles. The other portion of the inlet fluidenters fluid channels 53 and 54 to sweep out gas pockets around theunderside of the top cap 38 (FIG. 2 b). By creating a mechanical sealbetween the top cap 38 (FIG. 2 b) and the housing bowl 42 (FIG. 2 b), aflow path which allows fluid to travel beneath the top cap 38 (FIG. 2 b)and then back above on the opposite side through cut out 51 is generatedwith two channels 53 and 54.

FIG. 5 illustrates the two larger ribs 49 positioned a short distancebelow the top cap seal ridge 55 to direct the inlet fluid to sweep thebottom of bowl 42 (FIG. 2 b) and the underside of the top cap 38 (FIG. 2b).

FIGS. 6 a and 6 b illustrate the flow of liquid as shown by the arrows.The inlet fluid is directed down the side channel 46 created by ribs 49(FIG. 5) and sweeps the volume between the bottom of the filter media 40(FIG. 2 b) and the bottom inner surface of bowl 42. The fluid is alsodirected through channels 53 and 54 (FIG. 4 b) to sweep the underside ofthe top cap 38.

FIG. 7 illustrates the fluid flow as it is directed about the underside57 of the top cap 38 (FIG. 2 b) through second channel 33 (FIG. 2 b) onan increasing slope to eliminate gas bubbles.

FIG. 8 illustrates the converging flow paths to access point 48directing air bubbles through second channel 33, through cut out 51 andabove the top cap 38 (FIG. 2 b) into the volume between the top cap 38(FIG. 2 b) and the cover 36 (FIG. 2 b).

FIG. 9 illustrates the flow path being directed back above the top cap38 at the lowest location (nadir) 58 of the volume under the housingcover 36 (FIG. 2 b). This ensures that the liquid is forcing the gasbubbles along the underside of the top cap 38 (FIG. 2 b) to channel 31(FIG. 2 b).

FIG. 10 illustrates a housing cover 88 with a restricted fluid flow path71 is provided to prevent reverse fluid flow along channel 73. Therestricted flow path 71 allows critical surfaces to be swept during thevent process alone. During the vent process, only a small amount of thefluid entering the fluid inlet 93 is able to pass directly to the vent92 while the remainder of the fluid velocity is maintained to continuefluid flow below the top cap 81 (FIG. 11) of the filter cartridge 40(FIG. 2 b) and sweep the underside of the top cap 81. The fluid thenconverges to the access point 84 of the vent groove 73 where the fluidvelocity can be more easily maintained with a small cross-sectionalarea. In contrast, with unrestricted access to the gas vent 92, thesweeping of the cartridge must be done during the filtration process,thus being less effective than the vent process or both the vent andfiltration processes. The housing cover 70 is provided with vent 92,fluid inlet 93 and fluid outlet 75. Both inner surfaces 90 and 77 slopetoward gas vent ridge 87 to facilitate gas flow to gas vent 92. As shownin FIG. 11, the under surface 94 of top cap 81 is provided with gaschannel 83 which converges to access point 84 which is in fluidcommunication with channel 73 (FIG. 10). Top cap 81 also is providedwith outlet 85 which is in fluid communication with outlet 75 (FIG. 10).The top cap of FIG. 11 is bonded to housing cover 88 to block area 86thereby to reduce the hold-up volume and create the fluid flow paths ofthe filtration apparatus.

The present invention also provides a method for operating the liquidfiltration device of this invention in systems for filtering anddispensing process fluids. In a typical application (also called singlestage technology), filters are installed dry between a dispensemechanism (e.g. diaphragm pump, air pressurized canister, etc) and anoutlet nozzle that directs the fluid onto a substrate such as asemiconductor wafer or optical disc. To remove air from the filter'spores, the process fluid is pushed into the filter and flushed out boththe vent and the outlet ports until each fluid stream contains novisible air bubbles. Unfortunately, the fluid sent out the vent andoutlet contains many bubbles, and it is well known that bubbles cancause defects on or in a coated substrate. Therefore, this bubble-ladenfluid is normally directed to waste and not re-used, and this practicecan consume a significant amount of fluid. Process fluids can beexpensive ($1,000 to $10,0000 per liter) and minimizing waste by moreefficiently eliminating bubbles is important.

Typical filtration devices are not optimized to remove bubbles. Thepreferred operation orientation to remove bubbles uses the filter withthe fluid inlet at the bottom and the vent at the top. Although thisefficiently removes large gas bubbles from the device, smaller bubblesintroduced through the inlet rise slowly along the outside of themembrane. Purging these bubbles from the upstream side of the devicetakes considerable time and wastes fluid. In addition, bubbles can beabsorbed by the membrane, resulting in de-wet spots causing shorterfilter lifetime and bubble induced substrate defects.

With a TST system, a microprocessor controls the actions of two pumpswith a filter between them to allow for many process benefits. Thedesigns of these systems also allow for recirculation of bubble-ladenfluid to minimize the amount of fluid that is wasted during start-up ofa new filter. During start-up of a dry filter, fluid is pushed throughthe filter to the downstream side, where the bubble-laden fluid (fromgas removed from the pores of the filter membrane) is cycled back to theinlet of the pump. This fluid is then brought back to the upstream sideof the filter. Since the membrane pores are now filled with the processfluid, the membrane is a more effective (but not completely effective)barrier to bubble passage. In the prior art Impact LHVD filter, thebubble laden fluid is directed to the bottom of the filter. Bubbles mustthen rise by buoyant forces to the filter's vent where they are removedeither by an automatic means (software triggered vent valve) or by amanual means (manually actuated vent valve). Although this is a moreefficient method for removing bubbles from the filter and conservingfluid, waste is still generated, as the venting process is notoptimized. For all of these systems, bubble venting is not optimized asthe venting process releases not just bubbles but a bubble saturatedfluid stream. Since bubbles do not rise quickly in many process fluids,the motion of the fluid toward the vent is required to remove thebubbles (effectively, the bubbles are carried along by the fluidstream). In addition, the smaller the bubbles to be removed, the morefluid that is ejected in the stream.

Bubble venting with the liquid filtration device of this invention canuse an algorithm to automatically control the venting of filters (“smartventing”). Specifically, smart venting will limit the number of timesthat the filter undergoes a vent cycle, and it will limit the amount offluid that is lost during each vent cycle.

Typically, filters are vented during start-up and during operations asfollows:

(A) In a TST system during filter start-up, the filter is vented everyfifth cycle to remove entrapped bubbles. Typically, the vent valve opensfor 250 milliseconds, and approximately 50 to 150 microliters of fluidis sent to waste. During a typical start-up and preconditioning process,the filter can be vented more than 200 times. Therefore, this processwastes between approximately 10 milliliters and 30 milliliters of fluid.Also, during normal operation, the filter is vented every cycle, againresulting in between 50 and 150 microliters being lost per eachdispense.

(B) In non-TST applications, venting is usually a manual process and isat the discretion and convenience of the operator. During start-up,venting is more frequent, but the manual aspect of venting results inbetween 50 to 100 milliliters of fluid loss. Also, since there istypically no recirculation of the filter's downstream fluid, anadditional 500 to 1500 milliliters can be wasted conditioning thefilter. Finally, during operation, venting can be done once per day, andagain, between 20 and 30 milliliters can be lost each time.

With the liquid filtration device of this invention, smart venting isprogrammable and automated. On a single stage system, this could beaccomplished by using an “intelligent” manifold and the device of thisinvention. The current IMPACT ST manifold is a passive device, but itcan be made to do smart venting by adding a microprocessor and severalfluid connections (e.g., solenoid valves, tees). A description of such asystem is shown in FIG. 12. In this figure, the manifold with the filterdevice of this invention 70 controls the operation of solenoid ventvalve 72 and solenoid recirculation valve 74. The manifold with thedevice of this invention is also in communication with a pump 89. Teeconnection 76 is positioned so that fluid can be directed either throughrecirculation valve 74 or through the stop and suckback valve 78 to thesubstrate 84. Tee 80 is positioned both to accept fluid from fluidsource 82 during normal operation or from valve 74 when the fluid isrecirculated to the manifold and filter device 70. At start-up of a newfilter, recirculation valve 74 and stop and suckback valve 78 are closedand vent valve 72 is opened. Fluid is then sent into the manifold tofill the housing of the filtration device. After the housing is full,fluid can then be recirculated automatically while vent valve 72 isclosed and recirculation valve 74 is open so that vent loss can beminimized. At selected times during recirculation (either timed or aftera certain number of cycles), the recirculation valve 74 is closed andthe vent valve 72 is opened to remove gas from the manifold and filter70. After the filter has been primed, valve 74 is closed and valve 78 isopened so that fluid can be deposited on substrate 91.

In most cases, the number of cycles between venting could be lengthenedby using the device of this invention. Since bubbles are preferentiallytrapped and coalesce at the top of the filtration device, they are notin contact with or pass by the filter membrane. As such, they will notform de-wet spots (i.e., causing shorter filter lifetime or introducingbubble induced substrate defects). Therefore, the time between ventprocesses can be increased.

Also, the vent valve opening (time and geometry) can be minimized.Currently, the vent valve must be sufficiently open to allow forbubble-laden fluid to flow through the valve. However, since the bubbleswill coalesce into larger bubbles, air (with its lower viscosity) flowsmore easily than fluid through a small passage, and opening the ventever so slightly for a short time interval would allow air to passthrough while not allowing fluid to pass. This could be accomplished byeither setting a short vent opening time or controlling the vent valveto minimize its open orifice area. Both would be effective in minimizingthe opening of the valve for different viscosity fluids, and both wouldminimize fluid loss through the vent.

The automatic operation method of this invention can be further improvedby incorporation of the following features:

(A) Install a membrane contactor type of degasser in the system. Thisdegasser can be installed on the filter's vent line. Also, on a singlestage system, it can be upstream of the filter; and on a two stagetechnology system it is positioned on the upstream side of the pump (butdownstream of the line used to recirculate the fluid during start-up).Such a degasser remove bubbles and prevent microbubble formation withoutaffecting the fluid stream. This also has the advantage of practicallyeliminating venting during normal operation. Other degassing means(e.g., sparging, heating, vacuum, etc.) can be used, but those meansusually result in undesirable changes to the process fluid (e.g.,viscosity change due to solvent evaporation).

(B) Install a bubble detector either in the vent line, in the vent portof the filter itself or in the manifold that connects the filtrationdevice to a two stage technology system. Venting then can be enabledonly when the bubble detector senses a sufficient quantity of gas with asignal being read by a microprocessor. In addition, venting can becontrolled such that only bubbles are vented and not fluid.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A method of removing bubbles from a fluid passing through a filterdevice, comprising: providing a filter device comprising a housing, thehousing comprising a bowl, a cap, and a cover, the bowl defining anopening that receives a filter medium, the cap substantially coveringthe opening of the bowl and the filter medium, the cover being fitted tothe cap and the bowl, the cover including a fluid inlet, a fluid outlet,and a vent; directing fluid from the inlet toward the vent through afirst fluid channel defined in a first volume between the cover and thecap, the first fluid channel accumulating bubbles from the fluid nearthe vent as the fluid enters the filter device, the inlet and vent beingpositioned at the same end of the housing; and optionally, opening thevent to enable the bubbles that accumulate near the vent to be expelled.2. The method of claim 1 further comprising: directing the fluid fromthe first fluid channel to sweep an undersurface of the cap through asecond fluid channel, the second fluid channel being defined in a secondvolume between an undersurface of the cap and the filter medium, thesecond fluid channel accumulating bubbles from the fluid that collect orform near the undersurface of the cap; and further directing the fluidfrom the second channel back to the first fluid channel through anaperture defined in the cap that couples the second fluid channel withthe first fluid channel, the first fluid channel accumulating bubblesrecovered in the second fluid channel near the vent.
 3. The method ofclaim 2 further comprising: directing the fluid from the first fluidchannel toward the bottom of the bowl through a third fluid channeldefined between the bowl and the filtration medium, the third fluidchannel enabling the fluid to sweep the bottom of the bowl; and furtherdirecting the fluid from the bottom of the bowl through a plurality offourth fluid channels toward the second fluid channel.
 4. The method ofclaim 1 wherein the first fluid channel is characterized bycross-sectional areas that facilitate a fluid velocity that enablesremoval of bubbles from the fluid flowing through the first fluidchannel.
 5. The method of claim 1 wherein the first fluid channelextends substantially about the circumference of the housing cover, suchthat the first fluid channel spirals up from an outlet side of the coverto provide a pathway for bubbles to be directed to the vent.
 6. Themethod of claim 2 wherein the second fluid channel extends substantiallyabout the circumference of the cap, the second fluid channel defining aflow path allowing fluid to travel beneath the cap and then back abovethe cap through an aperture into the first fluid channel for expulsionthrough the vent.
 7. The method of claim 3 wherein the third fluidchannel is defined between at least two ribs positioned axially alongthe inside of the housing bowl.
 8. The method of claim 3 wherein theplurality of fourth fluid channels converge with the second fluidchannel at or near the nadir of the volume between the cap and the coverof the housing.
 9. The method of claim 8 wherein the plurality of fourthfluid channels are each defined between at least two ribs positionedaxially along the inside of the housing bowl.
 10. The method of claim 1wherein the underside of the cap has a sloped surface, the slopedsurface having a nadir and a zenith, the zenith being juxtaposed to thevent.
 11. The method of claim 1 wherein the housing cover has aninternal surface angled toward a vent side of the cover to provide apathway for bubbles to be directed to the vent.
 12. The method of claim1 further comprising: opening and closing the vent for time intervalsthat minimize fluid loss.
 13. The method of claim 1 further comprising:providing a degassing membrane contactor external to the filter deviceto further eliminate bubbles.
 14. A method of removing bubbles from afluid passing through a filter device, comprising: providing a filterdevice comprising a housing, the housing comprising a bowl, a cap, and acover, the bowl defining an opening that receives a filter medium, thecap substantially covering the opening of the bowl and the filtermedium, the cover being fitted to the cap and the bowl, the coverincluding a fluid inlet, a fluid outlet, and a vent; directing fluidfrom the inlet toward the vent through a first fluid channel defined ina first volume between the cover and the cap, the first fluid channelaccumulating bubbles from the fluid near the vent as the fluid entersthe filter device; further directing the fluid from the first fluidchannel to sweep an undersurface of the cap through a second fluidchannel, the second fluid channel being defined in a second volumebetween an undersurface of the cap and the filter medium, the secondfluid channel accumulating bubbles from the fluid that collect or formnear the undersurface of the cap; further directing the fluid from thesecond fluid channel back to the first fluid channel through an aperturedefined in the cap that couples the second fluid channel with the firstfluid channel, the first fluid channel accumulating bubbles recovered inthe second fluid channel near the vent; and optionally, opening the ventto enable the bubbles that accumulate near the vent to be expelled. 15.A method of removing bubbles from a fluid passing through a filterdevice, comprising: providing a filter device comprising a housing, thehousing comprising a bowl, a cap, and a cover, the bowl defining anopening that receives a filter medium, the cap substantially coveringthe opening of the bowl and the filter medium, the cover being fitted tothe cap and the bowl, the cover including a fluid inlet, a fluid outlet,and a vent; directing the fluid from the inlet of the filter devicetoward the bottom of the bowl through a first fluid channel definedbetween the bowl and the filtration medium, the first fluid channelenabling the fluid to sweep the bottom of the bowl; further directingthe fluid from the bottom of the bowl through at least one second fluidchannel toward the vent for removal of bubbles in the fluid; andoptionally, opening the vent to enable the bubbles that accumulate nearthe vent to be expelled.
 16. The method of claim 15 wherein the housingcover has an interior surface being angled toward the vent to enablebubbles removed from the fluid to rise to the vent.
 17. The method ofclaim 15 wherein an interior wall of the housing bowl is fitted to theexterior wall of the filter medium, such that the first fluid channel isdefined therebetween for directing the fluid from the inlet of thefilter device toward the bottom of the bowl.
 18. The method of claim 15wherein at least one flow channel is defined between the interior bottomof the housing bowl and the exterior bottom of the filter medium, suchthat at least one fluid channel is defined therebetween for sweeping theinterior bottom of the housing bowl.